Embedding element to be embedded in the end part of a windmill blade, a method producing such an embedding element as well as embedding of such embedding elements in a windmill blade

ABSTRACT

An embedding element ( 11 ) for embedment in the root of a wind turbine rotor blade ( 15 ) of a fibre composite material, said embedding element being elongated and having a first end portion ( 1 ) and a second end portion ( 2 ) and provided with fastening means, eg a threaded hole, a threaded rod or the like in its first end portion ( 1 ). Between its two end portions ( 1, 2 ) the embedding element ( 11 ) is provided with a first longitudinal lateral face ( 14 ) extending substantially concavely in a cross-sectional view perpendicular to the longitudinal axis of the embedding element, and with a second longitudinal lateral face ( 16 ) facing opposite the first lateral face ( 14 ) and extending substantially correspondingly convexly in a cross-sectional view perpendicular to the longitudinal axis. The invention further relates to a method of producing such an embedding element, a method of producing a wind turbine blade ( 15 ) of fibre composite material, a plurality of embedding elements ( 11 ) being embedded such in juxtaposition in the blade root that they follow the circumference of the root and the concave lateral face ( 14 ) of each embedding element ( 11 ) engaging the convex lateral face ( 16 ) of a juxtaposed embedding element and allowing access to the fastening means ( 24 ) from the outside.

TECHNICAL FIELD

The invention relates to an embedding element for embedment in the rootof a wind turbine rotor blade, said element being elongated and having afirst end portion and a second end portion and provided with fasteningmeans, eg a threaded hole, a threaded rod or the like in its first endportion.

The invention further relates to a method of producing such an embeddingelement, a method of producing a wind turbine rotor blade, in which aplurality of embedding elements are embedded, and a wind turbine rotorblade.

BACKGROUND ART

The fastening of fibre composite components, eg polymer components offibre glass or carbon fibres, which are subjected to loads from otherstructural elements, is often troublesome. One of these problems occurswhen a wind turbine blades is to be secured to the hub of the windturbine in such a manner that the connection therebetween is able totransfer heavy dynamic forces. The end face of a rotor blade root isoften circular and secured to a circular metal flange on the turbine hubby means of bolts or threaded rods.

U.S. Pat. No. 4,915,590 discloses several methods for attaching the rootof a wind turbine blade to a flange on the hub. The publication thusdiscloses a method, whereby the blade wall in the root is provided withembedded, elongated embedding elements in form of sucker rods comprisinga fibre glass rod, one end of the rod being provided with a coupling inform of a female-treaded steel bushing. The embedding elements areembedded such in the blade wall at the root that the female thread ofthe steel bushings is accessible from the end face of the blade root forattachment thereof to the hub.

One drawback of this method is that it is time-consuming to position theembedding elements accurately in the mould and subsequently theretoplace fibre mats in abutment with the element to ensure a durableembedment. Due to the circular shape of the rods, the fibre mats have tobe pushed downwards on either side, and even if this is achieved, foldsare created in the fibres/fibre mats which weaken the strength and whichin turn cause a risk of delamination due to the heavy dynamic loads.

DESCRIPTION OF THE INVENTION

The object of the invention is to provide a new and improved embeddingelement for embedment in a wind turbine blade made of fibre compositematerial allowing for a simplified embedment process and ensuringincreased strength at fixation of the wind turbine blade to the turbinehub.

According to the invention the object is obtained in that between itstwo end portions the embedding element is provided with a firstlongitudinal lateral face extending substantially concavely in across-sectional view perpendicular to the longitudinal axis of theembedding element, and with a second longitudinal lateral face facingopposite the first lateral face and extending substantiallycorrespondingly convexly in a cross-sectional view perpendicular to thelongitudinal axis. As a result it is possible to lay up the embeddingelements in alignment such that a concave lateral face engages a convexlateral face, whereby the positioning of the elements is facilitated.Due to the concavity/convexity the embedding elements may rotate inrelation to each about their longitudinal axis to allow adaptationthereof to various curve shapes, eg to the circular cross-sectionalshape of a blade root. The same type of embedding element may thus beused for blade roots of different diameters, the number of embeddingelements used naturally depending on the diameter. The embedding elementmay also be used for other composite components, such as aeroplane wingsfor securing these to the fuselage, said wings having a substantiallyelliptic cross section.

According to an embodiment the embedding element may have a taperingshape in the direction towards the second end, whereby the fibre lay-upmay be performed during the embedding process without causing sharpbends in the fibres or fibre mats in the transitional area between thesecond end of the embedding element and the composite component. If therigidity of the embedding element differs from that of the fibrecomposite material, a gradual transition in the rigidity of the finishedfibre composite component is also obtained.

According to a preferred embodiment the embedding element has an upperface and a lower face interconnecting the concave lateral face and theconvex lateral face, the upper face and the lower face extendinggradually convergently towards the second end portion of the embeddingelement to provide a wedge-shaped embedding element. As a result atapering shape is obtained, while ensuring that the longitudinal axes ofthe embedding elements extend in parallel.

According to a preferred embodiment the embedding element is madesubstantially of a fibre composite material, whereby a complete fibrecomposite component having homogenous material properties in relation torigidity and strength and thermal expansion is obtained.

The invention also relates to a method of producing the above embeddingelement, wherein an elongated core element, preferably of a fibrecomposite material and preferably made by pultrusion, is provided, afastening member being arranged at the first end of the core element andthe core element with the fastening member being secured inside a casingby means of adhesion, said casing including the concave and the convexlateral faces and preferably made of a fibre composite material,preferably by pultrusion. A solid embedding element may thus be producedin a simple manner by means of such a method.

According to a preferred embodiment of the method the first end of thecore element is conical and the inwardly facing end of the fasteningmember is provided with a corresponding conical recess or vice versa. Asa result, the two parts may be accurately fixed in relation to eachother and the embedding element is provided with a strong fixation andincreased strength.

According to an advantageous embodiment two embedding elements areproduced simultaneously by arranging a fastening member at either end ofthe core element prior to the encasement thereof inside the casing, andsubsequently making an inclined, plane cut from the upper face to thelower face or vice versa to produce two wedge-shaped embedding elements.This method offers a particularly simple manufacture of wedge-shapedembedding elements and is also advantageous in that safety checks may becarried out by measuring the tensile strength through the fasteningmeans in both end portions and in that a tensile test may be performedbefore the two elements are separated.

The invention further relates to a method of producing a wind turbinerotor blade of a fibre composite material, a plurality of embeddingelements being embedded such in juxtaposition in the blade root thatthey follow the circumference of the root cross section, which may becircular, and the concave lateral face of each embedding elementengaging the convex lateral face of a juxtaposed embedding element andallowing access from the outside to the fastening means which may beused for securing the blade to a flange on a wind turbine hub.

The invention also relates to a wind turbine made by means of such amethod.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail below with reference to theaccompanying drawings, in which

FIG. 1 is a partly sectional, perspective view of a first embodiment ofa blank from which two embedding elements are produced,

FIG. 2 is schematic view of a method of producing a core element for theblank shown in FIG. 1,

FIG. 3 is a schematic view illustrating the fastening of the fasteningmeans to the core element,

FIG. 4 is a schematic view of a pultrusion system for the manufacture ofthe blank shown in FIG. 1,

FIG. 5 is a schematic view illustrating the cutting of the blank shownin FIG. 1,

FIG. 6 is a sectional view of the blank shown in FIGS. 1 and 5 in itscut state,

FIG. 7 is a schematic view of how three embedding elements according tothe invention may be embedded in relation to each other in a fibrecomposite component,

FIG. 8 is a perspective view of the root of a wind turbine blade,embedded embedding elements according to the invention beingschematically shown,

FIG. 9 is a perspective view of an embedding element according to theinvention, and

FIG. 10 illustrates an alternative embodiment of an embedding elementaccording to the invention seen from the first end portion.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

FIGS. 1-6 primarily relate to a method of producing an embedding elementaccording to the invention. The embedding element is shown in aperspective view in FIG. 9 and includes an elongated body having a firstend portion 1 and a second end portion 2. The embedding element 11 has asubstantially planar upper face 18 and a planar lower face 19 parallelto the upper face. The planar upper face 18 passes into an inclinedsurface 66 extending downwardly towards the lower face 19 such that theembedding element becomes wedge-shaped and tapers towards the second endportion 2. The first end portion houses an embedded fastening member 22in form of a metal bushing with a threaded hole 24. The embeddingelement further has a concave, circular cylindrical lateral face 14extending in entire length of the embedding element and opposite thelateral face 14 a corresponding convex circular cylindrical lateral face16 also extending in the entire length of the embedding element.

As shown in FIG. 7, several embedding elements 11 may be arranged inparallel to allow the convex lateral faces 14 to engage the concavelateral faces 16 and such that the longitudinal axes of the elementsextend in parallel. Due to the concave and convex lateral faces, theembedding elements may extend along a curve, eg a circle, in a planeperpendicular to the longitudinal axes of the embedding elements 11.

FIG. 8 illustrates the root portion of a wind turbine rotor blade 15made of a fibre composite material. Schematically shown embeddingelements 11 are embedded in the root along the circumference thereofsuch to allow access to the threaded holes 24 of the embedding elements11 from the end face of the blade root.

Wind turbine blades are typically made by means of two blade shellhalves of fibre-reinforced polymer. When moulded the two halves areglued together along the edges and via two bracings, which prior theretohave been glued to the inner face of one the blade shell halves. Theother blade shell half is then arranged on top of bracings and gluedthereto and along the edges. The blade shell halves per se are typicallymade by vacuum infusion, in which evenly distributed fibres, rovings,which are fibre bunches, bands of rovings or mats, which may be feltmats of single-fibres or woven mats of fibre rovings, are layered in amould part and cover by a vacuum bag. By creating vacuum in the cavitybetween the inner face of the mould part and the vacuum cloth resin issucked into and fills the cavity containing the fibre material. Someform of fastening means are to be provided in the end face of the bladeroot in order to securely fix the blade to the wind turbine hub.

The embedding elements 11 according to the invention are particularlysuitable for the provision of fastening means in the end face of theblade root, as they are able to rotate in such a manner in relation toeach other due to the concave and convex lateral faces 14, 16 that theyabut each other regardless of the diameter of the blade root.

The embedment of the embedding elements 11 typically comprises thefollowing steps: Each of the embedding elements is secured to the rootflange of the mould part, said flange being a strong metal plate withapertures corresponding to the flange provided on the turbine hub onwhich the blade is to be mounted. A fibre glass mat is placed on theconvex lateral face 14 of each embedding element 11, said mat being cutinto shape before the next embedding element is secured. As a result asmall spacing is provided between embedding elements 11 allowing for asubsequent injection of resin between the embedding elements resultingin an improved embedment.

Due to the tapering shape of the embedding elements 11, a uniformmaterial transition from the embedding element to the other bladematerial, whereby stress concentrations are avoided.

FIG. 10 illustrates an optional embodiment, in which the first endportion 1 of each embedding element 11 is provided with two threadedholes at different distances from the upper face 18. This embodiment isadvantageous in that two bolt circles are obtained, whereby the diameterof the blade root may be reduced, which in turn reduces the costs of theturbine hub and the like.

A method of producing the embedding elements according to the inventionis explained in details below with reference to FIGS. 1-6.

FIG. 1 is a perspective and partly sectional view of a blank 10 for themanufacture of two embedding elements 11 according to the invention. Theblank 10 is formed substantially of a core element 12, two fasteningmembers 22, of which only one is visible, and an outer casing 18. Thecore element 12 is provided with conically tapered ends 20 fitting intoconical recesses 20′ in the fastening members 22, confer FIG. 3. Athrough-going hole 25 extends from the bottom of the conical recess 20′to the opposite outer end of the fastening member 22. A portion of thehole 25 is provided with a thread 24. The outer casing 18 has alongitudinal, concave, circular cylindrical lateral face 14 and alongitudinal, convex circular cylindrical lateral face 16 arrangedopposite the concave face 14.

FIG. 2 is a schematic view of how the core elements 12 are produced. Aportion of a pultrusion device 30 is shown, in which a string ofpultruded fibre composite material 32 extend. A saw 34 cuts the string32 into lengths corresponding to the length of each core element 12 anda cutting device shapes the ends 20 of the core element 12 such thatthey become conical.

FIG. 3 shows how the ends 20 of the core element 12 may be glued intothe corresponding recesses 20′ of the fastening members 22.

Having been glued to the ends of the core element 12, the fasteningmembers 22 are secured by screws by means of the threaded rods 28 toadditional core elements 12 with glued-on fastening members 22 so as toform a long rod.

FIG. 4 illustrates a pultrusion system 40 in which the above rod isinserted into a receiving station 46 jointly with bands of fibrematerial 42, 44, the assembled string 48 formed of the rod and the fibrematerial 42, 44 is then inserted into a heat and curing station 50.Resin is fed from a resin reservoir 52 into the heat and curing station50 and saturates the fibre material in the string 48. The saturatedstring 48 is passed through a nozzle 54 from which a pultrusion string56 extends, said string having a cross section corresponding to that ofthe blank shown in FIG. 1. The pultrusion string 56 is extracted fromthe nozzle by means of a pulling station 58. On the other side of thepulling station 58 a knife 60 cuts the pultrusion string 10 between twofastening members 22, whereby the blanks 10 are obtained. The threadedrods 28 may advantageously be made from plastic to facilitate thecutting action.

FIG. 5 illustrates how a saw 62 cuts through the blank 10 along aninclined cutting line 64 extending between the upper face 19 and thelower face 18.

FIG. 6 illustrates the cut blank 10 and how two embedding elements havebeen obtained, each with an inclined surface 64, 66.

In the method described above the casing 26 is provided by means of aso-called integral pultrusion process. It is, however, also possible toproduce the casing 26 separately in a pultrusion process and then gluethe core element 12 and the fastening member 22 onto the inside of thecasing 26.

As the embedding element, except for the fastening member 22, which ismade of steel, preferably is made of a fibre composite material, ahomogenous structure with homogenous material properties is obtained,when the embedding elements are embedded into the fibre compositematerial.

The invention is not restricted to the above embodiments. The embeddingelement 11 may also be made of for instance wood or plastic, and thefastening members 22 may also be made of plastic or wood. If theembedding element is not made of a fibre composite material, its wedgeshape contributes to forming a smooth transition between the materialproperties of the embedding elements and the properties of the materialinto which the embedding element is embedded.

The core element 22 and the fastening members 22 may formed integrallyand may thus include a rod with a threaded hole in one or both ends andbe made of metal, a fibre composite material, plastic or wood. The rodmay be glued into the casing 26, whereafter an inclined cut is made toform two embedding elements.

1. An embedding element (11) for embedment in the root of a wind turbinerotor blade (15) of a fibre composite material, said embedding elementbeing elongated and having a first end portion (1) and a second endportion (2) and provided with fastening means (24), in its first endportion (1), characterised in that between its two end portions (1, 2)the embedding element (11) is provided with a first longitudinal lateralface (14) extending substantially concavely in a cross-sectional viewperpendicular to the longitudinal axis of the embedding element, andwith a second longitudinal lateral face (16) facing opposite the firstlateral face (14) and extending substantially correspondingly convexlyin a cross-sectional view perpendicular to the longitudinal axis.
 2. Anembedding element according to claim 1, characterised in that it tapersin the direction towards the second end portion (2).
 3. An embeddingelement according to claim 2 characterised in that it is provided withan upper face (18) and a lower face (19) interconnecting the concavelateral face (14) and the convex lateral face (16), the upper face (18)and the lower face (19) extending gradually convergently in relation toeach other towards the second end portion (2) of the embedding elementto provide a wedge-shaped embedding element.
 4. An embedding elementclaim 1, characterised in that it is made of a fibre composite material.5. A method of producing an embedding element according to claim 1,characterised in that an elongated core element (12) is provided, that afastening member (22) including the fastening means (24) is arranged atthe first end portion of the core element (12) and that the core element(12) with the fastening member (22) is fixed inside a casing (26) bymeans of an adhesive, said casing including the concave lateral face(15) and the convex lateral face (16).
 6. A method according to claim 5,wherein the first end (20) of the core element (12) is conical and theinwardly facing end (20′) of the fastening member (22) has acorresponding conical recess or vice versa.
 7. A method according toclaim 5 of producing two embedding elements (11), wherein a fasteningmember (22) is arranged at either end of the core element (12) prior tobeing encased in the casing (26), an inclined, plane cut subsequentlybeing made from the upper face (18) to the lower face (19) or vice versato provide two embedding elements (11) of wedge shape.
 8. A method ofproducing a wind turbine rotor blade (15) of a fibre composite material,a plurality of embedding elements (11) according to claim 1 beingembedded such in juxtaposition in the blade root that they follow thecircumference of the root cross section, the concave lateral face (14)of each embedding element (11) engaging the convex lateral face (16) ofa juxtaposed embedding element and allowing access from the outside tothe fastening means (24) which may be used for securing the blade (15)to a flange on a wind turbine hub.
 9. A wind turbine blade (15) made bymeans of the method according to claim
 8. 10. A method according toclaim 1 wherein the fastening means comprises a threaded hole or athreaded rod.
 11. A method according to claim 5 wherein the elongatedcore element (12) comprises a fibre composite material.
 12. A methodaccording to claim 11 wherein the elongated core element (12) is made bya method comprising pultrusion.
 13. A method according to claim 5wherein the casing (26) is made of a fibre composition material.
 14. Amethod according to claim 13 wherein the casing (26) is mad by a methodcomprising pultrusion.
 15. A method according to claim 8 wherein thecircumference of the root cross section is circular.